U.S. Pat. No. 4,249,632 discloses a device for reducing the impact to pedestrians, which considerably reduces the magnitude of trauma to the head and upper body of a pedestrian. Such impact may occur upon striking the front hood of a motor vehicle during a collision. Referring to FIG. 29, discussion proceeds on this known device.
FIG. 29 illustrates a motor vehicle 1 equipped with this known device. In FIG. 29, a sensor 2 is suitably arranged in a zone of a front bumper bar of the vehicle 1 to detect a collision with a pedestrian. A front hood 3 can be pivoted around an essentially horizontally extending swivel pin placed at the front edge of the vehicle 1. The front hood 3 can be displaced by means of an air bag 5 that extends essentially across the entire width of the vehicle, so as to move it from a rest position indicated by one dot chain lines to an interception line indicated by full lines. In the rest position, the air bag 5 is folded and placed underneath the front hood 3, approximately in the zone under the cowl. The air bag can be inflated in the shortest possible time through a gas generator 4. The gas generator 4 may include a gas producing solid propellant charge that is ignited by means of the sensor 2 over a signal line.
JP-A 7-108902 discloses an air bag 5 that is inflated to extend over a front hood 3 of a vehicle 1. A sensor 2 is arranged in the zone of a front bumper bar of the vehicle 1. A gas generator 4 is placed underneath the front hood 3. When the gas generator 4 is activated by means of the sensor 2 upon a collision with a pedestrian, the air bag 5 is inflated, forming an impact buffer between the front hood 3 and the pedestrian.
Both of the devices are effective in reducing impact to the pedestrian's head upon detection of a collision. In the known devices, a pressurized gas is introduced into the air bag to inflate the bag to lift the front hood from the rest position to the interference position or to extend over the front hood. A large volume of gas is required, making it difficult to reduce the size of a gas generator. Thus, difficulty arises in placing the folded air bag and the gas generator underneath the front hood.
In the device according to JP-A 7-108902, the inflated air bag that extends over the front hood, creates an impact buffer upon detection of a collision with a pedestrian. When the pedestrian lands on the front hood during the collision, the head of the pedestrian, hit by the vehicle, contacts with the air bag. The stress of a direct impact to the head is the product of the magnitude of interference area through which the head contacts with the air bag and the magnitude of internal pressure of the air bag. The head is spherical so that the magnitude of stress, which the head is subject to, increases with the increasing magnitude of displacement. Thus, the air bag must have a considerable amount of vertical dimension to absorb the kinetic energy of the head. The air bag and the associated gas generator therefore become bulky, making it difficult to find installation space underneath the hood.
The art relating to reduction of impact to pedestrian is fairly well developed. However, a need remains for further development of such devices, especially in light of current movement to increased care of pedestrians involved in collision with a motor vehicle.